Gas turbines generally comprise a compressor, a combustor and a turbine. The compressor compresses air, which is then fed to a combustor to be used to burn a fuel. The resulting hot gas leaves the combustor and enters the turbine along a hot gas path. Usually, a ring of guiding vanes is arranged at the turbine inlet. To prevent compressed air from entering the hot gas path, seals must be provided at various places along the hot gas path. Especially, at the interface between the combustor and the turbine special honeycomb seals are used for sealing (see for example document U.S. Pat. No. 7,178,340).
The sealing situation at the combustor/turbine interface is shown in detail in FIG. 1. In FIG. 1, the hot gas path 40 guides hot gas 13 from a combustor 11 to turbine 12 of gas turbine 10 through the combustor/turbine interface. At the inlet of turbine 12 a circumferential ring of guiding vanes 14 is arranged. Each guiding vane 14 comprises an airfoil 17 extending in radial direction between an inner diameter platform 14a and an outer diameter platform 14b. The vanes 14 each are hooked into a support at the outer casing by means of a rear outer diameter hook 15 at the rear end of the outer diameter platform 14b (see upper circle in FIG. 1). Opposite to the rear outer diameter hook 15, there is a sealing arrangement 18 at the front end of the inner diameter platform 14a (see lower circle in FIG. 1), where a vane tooth 19 is in sealing engagement with honeycomb seal 20 (shown in even more detail in FIG. 2) and its sealing surface 21. The vanes 14 are supported on the inner platform by a holding structure 42. Transient thermal behaviour between the inner and the outer structure of the gas turbine lead to relative movement 43.
The particular requirement to the seal location or sealing arrangement 18 is that relative axial and radial movements have to be accommodated by the seal 20. This is supposed to be done via elastic deformation of the honeycomb. A tight sealing at the sealing arrangement 18 is important to prevent cooling air bypass around the combustor 11 into the hot gas path 40, leading to higher flame temperature and higher NOx emissions and to a larger degree of temperature non-uniformity at the turbine inlet of turbine 12. The problem is that ageing and deterioration wears the seal or the seal is plastically deformed. Both effects may lead to an increase of the leakage gap.